Different Sound on Same Part (Different Staff)

i was making a piece named "MUSIC FOR ORCHESTRA" some days. on one part, i wanted to make a cello part with 2 staff. the first staff is play arco, but the second staff play pizzicato. but when i place arco marking on the first staff, the second staff no longer play pizzicato anymore. can someone help me to find a solution for my problem ?

for better preview, i attach the screenshot of it below this text

thx ;)